Track circuit of great length

ABSTRACT

The disclosure relates to a track circuit for detecting the presence of a train on a long section of a railway track equipped with an AC traction power line, wherein the two rails of the section are insulated from the adjoining sections at each end thereof, comprising a generator connected to one end of the railway section for generating a voltage at a frequency which is approximately equidistant from the fundamental frequency of the power line and from the second harmonic thereof, the generated voltage comprising a series of pulse trains having a very low repetition rate. The track circuit also comprises a receiver for detecting the generated voltage at the opposite end of the railway section. The receiver includes an amplitude discriminator for eliminating the signals the amplitude of which is lower than a predetermined level and a selective demodulator which provides an output only when its input is energized by a signal at the above-mentioned repetition rate.

D United States Patent 1111 3,57 1,667

[72] Inventor Jean Demeur 3,075,127 1/1963 Secuwde et al. 3 7/147 Brussels, Belgium 3,246,142 4/1966 Duckitt et al 3l7/l47X [2g prz l- N 2 5 1969 3,252,141 5/1966 Galin 317/138 [2 i e r. 45 Patented Mar. 23, 1971 "Mary 3" [73] Assignee Ateliers de Constructions Electriques de Ammey Raymnd Roblc Charleroi (ACEC) Charm, ABSTRACT 111 d 1 1 t t k f Priority Mar- 14 1968 e 156 osurere a es 0 a trac c1rcu1t or de- Bel tectmg the presence of a tram on a long section of a railway track equipped with an AC traction power line, wherein the two rails of the section are insulated from the adjoining sections at each end thereof, comprising a generator connected to one end of the railway section for generating a voltage at a [54] TRACK CIRCUIT OF GREAT LENGTH frequency which is approximately equidistant from the funda- 7 Claims 4 Drawing Figs mental frequency of the power line and from the second har- 2 U S I monic thereof, the generated voltage comprising a series of {51} In} .(S /18127 pulse trains having a very low repetition rate The track circuit l Comprises a receiver f d t ti th generated lt 50 d is H01h47/20 at the opposite end of the railway section. The receiver in- 1 o earch 317/147 eludes an amplitude discriminator for eliminating the signals [561 :12212122158 3322;1zsitaizrgrsvtszfirs'xzsttr; 2 975 272 3/ T Z I PATENTS 7/ when its input is energized by a signal at the above-mentioned emc eta 31 147X repetition rate.

0 s o R A J F D A A1 D FA;

PATENTED m2 31971 FIG .I

F-DAy FIG. 2

IN VEN TOR Jean DEMEUR TRACK CiiRC UllT GREAT LENGTH-i This invention relates to a track circuit for detecting the presence of a train on a long section of a railway track equipped with an AC traction power line, wherein the two rails of of the section are insulated from the adjoining sections at each end thereof.

Track circuits are known comprising in a conventional manner a generator for producing a voltage between the two rails at one extremity of a railway section and a receiver at the other extremity of the railway section for energizing a railway relay which is operated when the axle of a vehicle short circuits the two rails. When the track circuit is very long, a certain number of conflicting conditions appear the most important of which concerns the frequency of the currents used in the track circuit. indeed, if the chosen frequency is high, the output voltage of the generator used must be high because of the high impedance of the railway line, which requires a generator having a high output railway rating. If, on the contrary, a lower frequency is used, the railway windings for the transmission of the traction current as well as the self inductances and the condensators used in the operation of generator and of the receiver take prohibitive dimensions. The frequency must also be such that it may not be confused with the stay frequencies and more particularly with the frequency of operation of the traction power line or of its harmonics.

The track circuit in accordance with the invention overcomes all the above-mentioned difficulties. It comprises a generator adapted to generate a voltage whose frequency is approximately equidistant from the fundamental frequency of the power line and from the second harmonic thereof, the generated voltage being in the fonn of trains of pulses at a very low repetition rate. The invention also comprises a receiver including an amplitude discriminator adapted to eliminate the signals the amplitude of which is lower than a predetermined level and a selective demodulator which provides an output only when its input signal is at said repetition rate.

The amplitude discriminator comprises two magnetic circuits having rectangular hysteresis characteristics. The first one of said magnetic circuits has a single winding and the second one of said magnetic circuits has a first and a second winding operating as a transformer, the single winding of said first magnetic circuit having more turns than the first winding of the second magnetic circuit. The single winding of the first magnetic circuit is connected in series with the first winding of the second magnetic circuit and both windings receive the input voltage while the output voltage is provided by the second winding of the second magnetic circuit.

The demodulator comprises an input transformer having a primary winding to which is applied the input of the circuit and two secondary windings the first one of which feeds a first winding of a magnetic circuit having a rectangular characteristic. A second winding of the last-mentioned magnetic circuit feeds an output transformer through a first winding of a second magnetic circuit having a rectangular characteristic. A second winding of the last-mentioned second magnetic circuit is fed in series with a third winding of the last-mentioned fist magnetic circuit by the output current of a transistor the base of which is fed through a potentiometer by the output voltage of the second secondary winding of the input transformer. Means are also provided to equalize the current of the transistor in the two windings that such transistor feeds.

The invention will now be disclosed with reference to the accompanying drawings in which:

FIG. 1 illustrates schematically a circuit for generating a voltage applied between two rails of a railway section;

FllG. 2 illustrates schematically a circuit for receiving the voltage generated by the generator;

FllG. 3 illustrates an embodiment of an amplitude discriminator; and

Fit}. 4 illustrates an embodiment of a demodulator for use with the invention.

FllG. It iliustrates schematically an arrangement of a generator adapted to feed a voltage which is applied between the two rails of a long railway section electrically insulated from the adjoining sections, such long railway section forming part of a railway track equipped with an AC traction power line. It comprises a pilot oscillator connected to a separator stage S having a high input impedance so as not to interfere with the stability of the oscillator O. The separator synchronizes a relaxation oscillator 0R which in turn feeds a power amplifier A the output voltage V of which feeds the two rails at one extremity of a railway section not shown. The output current of the amplifier A acts on the amplitude of the output current of relaxation oscillator 0R through a regulator Rg the input of which is connected to a modulator M which causes the generation of trains of pulses by the relaxation oscillator OR for a certain duration and at a predetermined repetition rate, these two parameters being separately regulated and the regulator Rg being used to maintain the input current of amplifier A within limits compatible with the good operation and the absence of overload on the transistors forming part of such amplifier. in the present example, the frequency of the traction power line being 50 Hz, the frequency of the oscillator 0 and consequently the frequency of output voltage V is 73 Hz., which is the mean value between the fundamental frequency and the second harmonic of the traction power line.

Fig. 2 illustrates schematically the receiver which is located at the extremity of the railway section which is opposed to the generator, Such receiver is fed by the input voltage E appearing between the two rails and filtered by a filter F which blocks the undesired frequencies located on each side of the useful frequency of 73 Hz. and more particularly the frequencies of 50 and Hz. The output of filter F is connected to an amplitude discriminator DA which will be described more fully in a later part of the disclosure. Such discriminator eliminates the signals the amplitude of which is lower than a predetermined level and is followed by an electronic multivibrator B providing rectangular signals which, after amplification by an amplifier A,, are demodulated by a circuit D which will equally be disclosed more fully in a later part of the application. The demodulated signals, after amplification by an amplifier A are applied to a railway relay R through a rectifier RD.

The amplitude discriminator DA of FIG. 2 is illustrated in FIG. 3. It comprises two saturable reactors T01 and T02 having windings the number of turns of which is n, and n respectively. The saturable reactor T01 has a single winding only but the saturable reactor T02 also has a second winding providing an output voltage U The single winding of saturable reactor T01 and the first winding of saturable reactor T02 are connected in series. The number of turns n of saturable reactor T01 is higher than the number of turns n of saturable reactor T02 and, as these two saturable reactors have rectangular magnetic characteristics, as soon as the current in the two windings in series reaches a predetermined valve, such current saturates reactor TOll but not T02. The result of this is that the impedance of the single winding of T01 is rendered practically nul and that the voltage U, applied to these two windings in series is applied mainly to the first winding of reactor T02 which consequently provides a maximum output voltage U, across the second winding thereof. If the amplitude of voltage U is too low, there is practically novoltage U Consequently, the amplitude discriminator eliminates the action of the voltages which are too low and among which are located the different voltages originating from the traction power line which voltages are, as explained previously, substantially blocked by the filter F.

E10. 4 illustrates schematically an embodiment of the demodulator D of H0. 2. It comprises two saturable reactors T03 and T04 made of a material having a rectangular magnetic characteristic. The first saturable reactor T03 has three windings n in, and the second saturable reactor T04 has two windings n, and a The demodulator receives its input voltage from a transformer TlRi having two secondary windings the first one of which feeds the winding n through a resistor r and the second one of which is connected to a potentiometer P the function of which will be explained later. Winding n of reactor T03 feeds the primary of output transformer TR2 through the winding n, of saturable reactor T04. A transistor T connected to a biasing source AL has its base emitter circuit fed by the potentiometer P and its collector current flows through the windings n, and n in series with a filtering self inductance L. A condensator C having a high capacity is used to equalize the variation of the collector current of transistor T because its base is fed by an alternating current. It is obvious that when an alternating voltage which is not modulated is applied to the primary of transformer TRll, for a predetermined regulation of potentiometer P, there is obtained a maximum emitter current in transistor T and this current is lowered more and more as the generated voltage is modulated by pulse trains of shorter duration and consequently with longer time intervals between such trains of pulses because, as it has been mentioned previously, the repetition rate is constant. If the collector current of transistor T is low, reactors T03 and T04 are not saturated; reactor T03 operates as a transformer but, because reactor T04 is not saturated, the winding n which has been specially designed for that purpose has a very high reactance so that the output voltage provided by transformer TR2 is low. if the collector current of transistor T is increased, there is a time where reactor T03 is still not saturated but where reactor T04 is saturated. The reactance of winding n is lowered to almost zero and the output voltage of transformer TR2 is high. if the collector current of transistor T is still increased, reactor To3 is also saturated and the coupling between windings n, and n is lowered and consequently the output voltage of transformer TR2 is also lowered. The elements of the circuit and the regulation of potentiometer P are established in such a way that the demodulator provides an output voltage at the predetermined frequency of modulation of the generator. For the other frequencies of modulation of the pulse trains and for a continuous voltage generation, the output is negligible. it is important to not that the circuit illustrated in MG. 4 is fool proof because any accidental defectiveness of one of the elements thereof results in the absence of an output voltage.

it is obvious that all the elements which are not disclosed in detail in the application may be realized in any known way and that various embodiments of the circuits disclosed may be thought of without departing from the spirit of the invention.

1 claim:

l. A track circuit for detecting the presence of a train on a long section of a railway track equipped with an AC traction power line, wherein the two rails of the section are insulated from the adjoining sections at each end thereof, comprising an alternating current generator connected to one end of the railway section for generating a voltage the frequency of which is approximately equidistant from the fundamental frequency of the traction power line and its second harmonic, the generated voltage consisting of a series of trains of pulses having a very low repetition rate, and a receiver adapted to receive the voltage generated by said generator located at the other end of said railway section and including an amplitude discriminator for eliminating the signals the amplitude of which is located below a predetermined level and a selective demodulator for providing an output voltage only when its input signal is at said repetition rate.

2. A track circuit as defined in claim 1, wherein the amplitude discriminator comprises two magnetic circuits having rectangular magnetic characteristics, the first one of said magnetic circuits having a single winding, the second one of said magnetic circuits having a first and a second windings, the single winding of said first magnetic circuit having more turns than the first winding of the second magnetic circuit, the single winding of said first magnetic circuit and the first winding of said second magnetic circuit being connected in series and receiving the input voltage while the output voltage is provided by the second winding of the second magnetic circuit.

3. A track circuit as defined in claim I, wherein said demodulator comprises a transformer having a primary winding for receiving an input voltage and two secondary windings a irst magnetic circul having a rectangular charac enstic an having a first winding connected to the first one of said secondary windings, said first magnetic circuit having a second winding connected to an output transformer; a second magnetic circuit having a rectangular characteristic and having a first winding connected in the input of said output transformer, said second magnetic circuit having a second winding connected in series with a third winding of said first magnetic circuit; a transistor connected to the second winding of said second magnetic circuit and the third winding of said first magnetic circuit; and a potentiometer having a first and a second terminals connected to the second one of said secondary windings, and an intennediate terminal connected to the base of the transistor.

4. A track circuit as defined in claim 3, wherein means are provided to equalize the current of said transistor in the second winding of said second magnetic circuit and the third winding of said first magnetic circuit.

5. A track circuit as defined in claim 1, wherein said generator comprises a pilot oscillator; and separator stage connected to said pilot oscillator; a relaxation oscillator connected to said separator; a power amplifier connected to the output of said relaxation oscillator for providing the output voltage applied to the railway section; a regulator connected to the output of said amplifier, said regulator being responsive to a modulator for causing said relaxation oscillator to generate trains of pulses lasting a predetermined time duration with a predetermined time interval between each train of pulses.

6. A track circuit as defined in claim 5, wherein the frequency of the pilot oscillator is 73 Hz.

7. A track circuit as defined in claim 1, wherein said receiver comprises a filter adapted to block the fundamental and the second harmonic of the traction power line, the amplitude discriminator being connected to the output of said filter; an electronic multivibrator connected to the output of said amplitude discriminator; an amplifier connected to the output of said electronic multivibrator, the demodulator being connected to the output of said amplifier; a second amplifier connected to the output of said demodulator; a rectifier connected to the output of said second amplifier; and a railway relay connected to the output of said rectifier. 

1. A track circuit for detecting the presence of a train on a long section of a railway track equipped with an AC traction power line, wherein the two rails of the section are insulated from the adjoining sections at each end thereof, comprising an alternating current generator connected to one end of the railway section for generating a voltage the frequency of which is approximately equidistant from the fundamental frequency of the traction power line and its second harmonic, the generated voltage consisting of a series of trains of pulses having a very low repetition rate, and a receiver adapted to receive the voltage generated by said generator located at the other end of said railway section and including an amplitude discriminator for eliminating the signals the amplitude of which is located below a predetermined level and a selective demodulator for providing an output voltage only when its input signal is at said repetition rate.
 2. A track circuit as defined in claim 1, wherein the amplitude discriminator comprises two magnetic circuits having rectangular magnetic characteristics, the first one of said magnetic circuits having a single winding, the second one of said magnetic circuits having a first and a second windings, the single winding of said first magnetic circuit having more turns than the first winding of the second magnetic circuit, the single winding of said first magnetic circuit and the first winding of said second magnetic circuit being connected in series and receiving the input voltage while the output voltage is provided by the second winding of the second magnetic circuit.
 3. A track circuit as defined in claim 1, wherein said demodulator comprises a transformer having a primary winding for receiving an input voltage and two secondary windings; a first magnetic circuit having a rectangular characteristic and having a first winding connected to the first one of said secondary windings, said first magnetic circuit having a second winding connected to an output transformer; a second magnetic circuit having a rectangular characteristic and having a first winding connected in the input of said output transformer, said second magnetic circuit having a second winding connected in series with a third winding of said first magnetic circuit; a transistor connected to the second winding of said second magnetic circuit and the third winding of said first magnetic circuit; and a potentiometer having a first and a second terminals connected to the second one of said secondary windings, and an intermediate terminal connected to the base of the transistor.
 4. A track circuit as defined in claim 3, wherein means are provided to equalize the current of said transistor in the second winding of said second magnetic circuit and the third winding of said first magnetic circuit.
 5. A track circuit as defined in claim 1, wherein said generator comprises a pilot oscillator; and separator stage connected to said pilot oscillator; a relaxation oscillator conNected to said separator; a power amplifier connected to the output of said relaxation oscillator for providing the output voltage applied to the railway section; a regulator connected to the output of said amplifier, said regulator being responsive to a modulator for causing said relaxation oscillator to generate trains of pulses lasting a predetermined time duration with a predetermined time interval between each train of pulses.
 6. A track circuit as defined in claim 5, wherein the frequency of the pilot oscillator is 73 Hz.
 7. A track circuit as defined in claim 1, wherein said receiver comprises a filter adapted to block the fundamental and the second harmonic of the traction power line, the amplitude discriminator being connected to the output of said filter; an electronic multivibrator connected to the output of said amplitude discriminator; an amplifier connected to the output of said electronic multivibrator, the demodulator being connected to the output of said amplifier; a second amplifier connected to the output of said demodulator; a rectifier connected to the output of said second amplifier; and a railway relay connected to the output of said rectifier. 